for example. But I have no idea if this is just my English brain "leaking" into Portuguese...

I'd be interested in answers that follow the literal meaning (i.e. it's not possible to capture in words) or ones that come from a different angle but are essentially idiomatic ways of saying "It's really really really [adjectivo]"

I just made an edit suggestion to your question. I see that you are an experienced SE user, so you must be familiar with the rollback function. If you disagree with the edit, hit the button.
– Ramon MeloMar 9 '17 at 5:17

what's the specific problem with the example sentence I gave? I looked on linguee and found a bunch of stuff like it, but a lot of that could also be bad translations from English linguee.com/english-portuguese/…
– Some_GuyMar 8 '17 at 16:48

Yes, you can say in Portuguese that there are no words, or that you have no words, to express something ("Não há palavras", "não tenho palavras"). You can't say that "words fail", though. You may say that words cannot or do not express something ("palavras não podem expressar/dizer", "palavras não expressam/dizem"). Or you can say that words are not enough ("palavras não bastam" or "palavras são insuficientes" or "palavras não dão conta").

But you cannot translate "how" into "como" always; if it has a quantitave implication, it is probably better translated as "quanto" or "o quanto":

Also, fronting a predicative like in English ("how grateful I am") is not always trivial. Peculiarly, you can say "como eu estou agradecido", or "quão agradecido eu estou" but never "como agradecido eu estou").

Portuguese has synthetic superlatives, too:

"Fico gratíssimo pela ajuda de vocês."

But their use is quirky (for instance, "agradecidíssimo" would be quite unusual, though the non-superlative "agradecido" is by far more common than "grato"), and standard and colloquial forms often diverge ("caríssimo" vs "carésimo").

The usual analytical way to express a superlative is through the adverb "muito" (much):

"Estou muito agradecido."

And a few adverbs, including "muito", also accept synthetic superlatives, you can also say,

"Estou muitíssimo agradecido."

But any adverb that can express intensification can be used, though with some implications on (in)formality: